The present invention relates to blow molding equipment and more particularly to apparatus for transferring preforms to a blow molding machine.
Various forms of molding devices have been developed for the formation of plastic bottles. In one approach, polyethylene terethalate preforms or parisons are first injection molded. The preforms may have a threaded neck and a cap locator or flange. Prior to blowing, the preforms are reheated to the blowing temperature of the plastic and then transferred from an oven to the blow station of a blow molding machine. The blow station includes a vertically split blow mold defining a plurality of cavities and a blow head assembly. Once the preforms are positioned within the two-piece mold, the mold is closed. The blow head delivers high pressure air to the preforms to blow mold the bottles. After molding, the mold is opened and the formed bottles are ejected from the machine.
Many different types of parison or preform transfer mechanisms have been developed. U.S. Pat. No. 4,011,039 entitled "PARISON TRANSFER DEVICE" issued on March 8, 1977, to Oas et al discloses a transfer device for moving parisons or preforms from a heating oven to a mold station. The device includes a carriage having a pair of picker assemblies for grasping and removing separate parisons from the oven. An example of another parison transfer device may be found in U.S. Pat. No. 4,313,720 entitled "PARISON TRANSFER MEANS" and issued on Feb. 2, 1982, to Spurr.
In a still further approach, a transfer or shuttle mechanism includes a plurality of jaw sets arranged side by side on a frame structure. Air cylinders open and close the jaws. Another air cylinder shifts the frame relative to a blow mold station. This basic structure is illustrated in U.S. Pat. No. 4,310,282 entitled "DELAY STRETCH AND BLOW MACHINE SYSTEM" and issued on Jan. 12, 1982, to Spurr et al.
Many of the prior preform or parison transfer mechanisms have been fairly complicated. The complexity has reduced reliability and placed limitations on production rates. In addition, problems have been experienced with proper handling of misformed preforms. Existing devices are unable to handle properly a set of preforms when one or more are of differing diameter. A need, therefore, exists for a preform transfer mechanism which will efficiently and effectively locate and receive preforms from an oven, transfer a set of preforms to a blow mold station and remove the formed product from the station at the completion of the molding operation.